Apparatus for equalized induction heating of workpieces



- 1949 H. A. STRICKLAND, JR

APPARATUS FOR EQUALIZED INDUCTION HEATING OF WORKPIECES Flled Apnl 12,1945 *PICIL PICI 2 RIGID".

l N V EN TOR Harold A. SUE/(land, Jr. W WQJW Q A TTORNE Y Patented Dec.6, 1949 UNITTED- Se'IZATESJQ PATENT OFFICE.

APPARATUS. EOR- EQUALIZED-INDUCTION HEATING OF WORKPIECES.

Harold A. Strickland; Ji-., Detroit; Mich, assi'gnor,

by mesne assignments, to The. OhioCrankshath Company, Cleveland, Ohio, acorporation of Ohio Application April 12, 1945, Serial No. 587,986

nace of this type is generally satisfactory where the workpiece isuniform in-shape; for example,

cylindrical, but where the workpiece is not uni-- formly shaped as, forexample, where the diameter of the central section of the workpiece isless than the diameter of the ends, this type of furnace may not besatisfactory as it may produce overheating of the central section.

A primary object of the present invention is to provide apparatus andcircuit arrangements which may be utilized in connection with a heatingcoil to modify the energy available for heating along the length of theheating coil so as to conform to variations in the substance of theworkpiece along the axis of the heating coil.

Still another object of the invention is to provide effective adjustingmeans for the energy output of a heating coil along its length which maybe applied to usual existing furnace types without difficulty.

An object also is to provide energy adjusting means which may readilyutilize alternative apparatus to accomplish the desired results.

Further objects will appear on consideration of the apparatus andcircuit of an embodiment of the invention hereinbelow set forth andillustrated in the accompanying drawing, in which:

Figure l is an elevation of an induction heating coil unit with thecontrol unit connected therewith;

Figure 2 is a diagrammatic showing of inductive means for controllingthe energy flow along the coil axis;

Figure 3 shows a workpiece of irregular shape.

Referring to Figure 1, there is shown in outline an induction furnace Iwhich includes the usual heating coil 2 of uniformly dimensioned andspaced turns surrounding a heating chamber 3. The heating coil isexternally and internally lined with fire-proof insulation layers 4 and5 and the furnace chamber is lined with fire-brick 6 supported bytubular cooling rails I. These rails are provided with support lugs 8for holding the workpiece 9 in position within the chamber.

The coil is provided with a plurality of taps II] which extend outwardlyat the side of the furnace. The furnace coil and accessory parts aresupported on asbestos composition end plates II and I2 5 Claims. (01.219-13) I asiindicatedi Alternating: currentsiszsupplied' from llf sinceboth-pairs of asbestos composition support asource, preferably, of'highfrequency current- In" order to 'secure'the variation. in energy out.-putof'tlie induction h'eatings'coil Ifor' heating are ticles ofirregular-shape; I utilize asecond coil enerally indicated by thenumeral I3 which is mounted'directly' above the furnace. Thisauxiliaryunitacomprises a-singlecoil" Ii -provided with taps I5 and supported byendplates I6 and IL the other as shown. Electrical connection is madebetween the two coils through the connectors I8 and I9 each of which isformed of a flat metal strip centrally apertured at one end and slottedat the other end so that the plate may be pivotally mounted on eitherthe upper or lower taps and detachably connected to one or more of thetaps in the other unit.

In operation, the main heating current is passed through the heatingcoil as between points 20 and 2| of Figure 2. The applied voltage andfrequency may be constant in value so that a uniform heat supply isavailable for a uniformly dimensioned cylindrical workpiece. Should,however, an irregular workpiece such as shown in Figure 3 and in dottedoutline in Figure 1, be placed in the furnace chamber, it becomesnecessary to reduce the heat output in the section 22 of lesser diameteras opposed to sections 23 and 24 of full diameter. This is accomplishedby connecting the upper ends of the connectors I8 and I9 to a selectedlength of inductor coil I4 and the lower ends of the connectors to tapsopposite the ends of section 22 so that the portion of the heating coilwhich encloses section 22 of the workpiece and is operative for heatingthe same is by-passed by the parallel connection of inductor I3. Thisparallel connection effectively reduces the current flow in the furnacecoil section opposite section 22 of the workpiece so that the heatingeffect is minimized to the point of safe and adequate temperature forthe desired purposes.

As indicated in Figure 2 and by the taps I5 in Figure 1, the inductor I3is variable so as to obtain variation in the impedance of the shuntcircuit. By utilizing an inductor shunt instead of a resistor, the powerloss is substantially reduced. A related advantage of the inductor shuntfor the specified purpose lies in its employment as a flux return forthe heater coil, the coil turns of the impedance in shunt with selectedsections of the heating coil, without disturbing the ,main heating coilcircuit, applicant is able to secure any de-.

sired variation of heat energy input to the work piece and this may beaccomplished readily with out important modification of the standardheating coil arrangement.

The showing as made is diagrammatic and hence no limitation is impliedthereby otherz-than may be required by the scope of the claims heretoappended.

What is claimed is:

1. In combination, an electric induction heating coil wound in a singledirection and having connections to an electric power source, saidcoil-having a plurality of taps intermediate said connections and aninductance coil connected across at least a pair of said tapsintermediate said connections, whereby to reduce the heatingjeffect ofthe heating coil between the taps connected tosaid inductance coil;

2. The combination of claim 1 wherein'said inductance coil has avariable inductance.

3. The combination of claim 1 wherein said inductance coil has aplurality of taps along its length adapted to be selectively connectedto the taps of said heating coil.

4. The combination of claim 1 wherein the flux field of the inductancecoil is opposite to the flux fieldof the heating coil and the inductancecoil is positioned exteriorly of and adjacent to the heating coilwhereby the flux fields may be additive.

5. The combination of claim 1 wherein said inductance coil is wound inan opposite direction to said heating coil and said coils are disposedin adjacent relationship with their axes substantially parallel.

HAROLD A. STRICKLAND, J R.

REFERENCES CITED The 'iollowing references are of record in the file ofthis patent;

UNITED STA ES P-A'I'ENTS Number Name Date 1,791,934 Northrup Feb. 10,1931 25%: 1,834,725 Northrup Dec. 1, 1931 1,943,802 I Northrup Jan. 16,1934 1,946,876 Northrup Feb. 13, 1934 2,308,043 Bierwirth Jan. 12, 19432,383,992 Sherman Septv 4, 1945 Kennedy Oct. 26, 1948

